AU-rich elements (AREs) present in the 3'untranslated
region of mature lymphokine and cytokine mRNAs regulate
mRNA stability and translational efficiency. Based on
their sequence features and functional properties AREs
can be divided into three classes. Class II AREs direct
asynchronous cytoplasmic deadenylation (processive kinetics)
generating poly-A(-) mRNAs. Among mRNA with class II ARE in
their 3' UTR are GM-CSF, IL-2.The minimum number of AUUUA
tandem motifs to activate processive degradation is 4
(of which at least 3 in tandem).
Furthermore, an AU-rich region 20-30 nt long immediately
5' to the cluster of AUUUA motifs can greatly enhance
the degradation activity.